kconfig: Add scripts/Kconfig.include from v4.19

As part of re-syncing our Kconfig logic up to v4.19, we had missed
adding this new file that includes helper macros.  To quote the upstream
commit e1cfdc0e72fc ("kconfig: add basic helper macros to scripts/Kconfig.include"):

Kconfig got text processing tools like we see in Make.  Add Kconfig
helper macros to scripts/Kconfig.include like we collect Makefile
macros in scripts/Kbuild.include.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Tom Rini <trini@konsulko.com>

Kconfig

@@ -5,6 +5,8 @@
 #
 mainmenu "U-Boot $(UBOOTVERSION) Configuration"
 
+source "scripts/Kconfig.include"
+
 # Allow defaults in arch-specific code to override any given here
 source "arch/Kconfig"
 

scripts/Kconfig.include

+# Kconfig helper macros
+
+# Convenient variables
+comma       := ,
+quote       := "
+squote      := '
+empty       :=
+space       := $(empty) $(empty)
+dollar      := $
+right_paren := )
+left_paren  := (
+
+# $(if-success,<command>,<then>,<else>)
+# Return <then> if <command> exits with 0, <else> otherwise.
+if-success = $(shell,{ $(1); } >/dev/null 2>&1 && echo "$(2)" || echo "$(3)")
+
+# $(success,<command>)
+# Return y if <command> exits with 0, n otherwise
+success = $(if-success,$(1),y,n)
+
+# $(cc-option,<flag>)
+# Return y if the compiler supports <flag>, n otherwise
+cc-option = $(success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null)
+
+# $(ld-option,<flag>)
+# Return y if the linker supports <flag>, n otherwise
+ld-option = $(success,$(LD) -v $(1))
+
+# gcc version including patch level
+gcc-version := $(shell,$(srctree)/scripts/gcc-version.sh -p $(CC) | sed 's/^0*//')